Your statement :
      @bar expands to a list of its elements, with anonymous undefined values in place of nonexistent elements
is negated by the code I posted. If "nonexistent elements" were indeed passed, assigning values to the corresponding aliases would vivify, in the original array. This is not the case.

You misunderstood me. I said nonexistent elements are not passed, and that anonymous (i.e. not bound to the array in any way) undefined values are passed in their place.